Waist Measurement May Catch Obesity BMI Alone Misses

A simple waist measurement may identify unhealthy levels of body fat that body mass index misses, according to a Rutgers Health study published in JAMA Network Open. The analysis found that waist circumference, either alone or combined with BMI, performed about as well as a newer framework requiring multiple body measurements.

Researchers examined data from 1,900 U.S. adults ages 20 to 59 who participated in the National Health and Nutrition Examination Survey. They compared several obesity-screening approaches with a highly accurate method for determining body fat.

The more complex framework combined BMI, waist circumference, waist-to-height ratio and waist-to-hip ratio. Although that approach identified more people with excess body fat, the Rutgers team reported that simpler methods achieved a similar level of accuracy. BMI or waist circumference provided a balance between identifying people who met body-fat criteria for obesity and limiting false-positive classifications. Waist circumference alone performed nearly as well.

The findings are relevant because BMI reflects weight relative to height but does not capture differences in body composition or where fat is stored. Waist circumference can provide information about fat distribution that BMI does not show, according to the researchers.

BMI used on its own also failed to identify a substantial number of people who met the study’s body-fat criteria for obesity. The result adds to concerns about using BMI as the only measure in obesity screening, although the study did not establish that waist measurement directly predicts diabetes, heart disease, stroke or cancer outcomes.

A waist-to-hip ratio requires recording hip circumference, a measurement the researchers said is rarely collected during routine clinical visits. Waist circumference is simpler to obtain and is increasingly included in clinical guidelines, the study team reported. That practicality could make it easier to incorporate into routine screening.

Lead author Aayush Visaria said that changes such as needing looser clothing may be an early indication of increased body fat, while noting that clothing size is not a substitute for a proper waist-circumference measurement. The researchers said their findings could inform future obesity-screening recommendations and support more routine use of waist measurements in health care.